Stress dependence of growth mode change of epitaxial layered cobaltite γ-Na0.7CoO2

We report stress dependence of growth characteristics of epitaxial γ-Na_0.7CoO₂ films on various substrates deposited by pulsed laser deposition method. On the sapphire substrate, the γ-Na_0.7CoO₂ thin film exhibits spiral surface growth with multi-terraces and highly crystallized texture. For the γ-Na_0.7CoO₂ thin film grown on the (1 1 1) SrTiO₃ substrate, the nano-islands of ∼30 nm diameter on the hexagonal grains are observed. These islands indicate that the growth mode changes from step-flow growth mode to Stranski-Krastanow (SK) growth mode. On the (1 1 1) MgO substrate, the large grains formed by excess adatoms covering an aperture between hexagonal grains are observed. These experimental demonstrations and controllability could provide opportunities of strain effects of Na_xCoO₂, physical properties of thin films, and growth dynamics of heterogeneous epitaxial thin films.     

Misfit driven azimuthal orientation of NaCl domains on Ag(1 0 0)

We investigated the growth of thin NaCl films on Ag(1 0 0) by spot-profile-analysis low energy electron diffraction (SPA-LEED), varying extensively the growth temperature (200–500 K) and the film thickness (0.5–14 ML). The incommensurate growth of NaCl on Ag(1 0 0) yields (1 0 0)-terminated epitaxial NaCl domains, which are preferentially oriented with their [0 1 0] axis parallel to that of the substrate. At 300 K, the NaCl domains exhibit an azimuthal mosaicity by 14° around this orientation and the NaCl unit cell is laterally contracted in the first layers by 0.9% with respect to the bulk. At higher growth temperatures, the azimuthal mosaic distribution sharpens and additional distinct orientations appear, presumably due to a higher-order commensurability. The evolution of the azimuthal mosaic distribution with increasing temperature can be ascribed to both the NaCl thermal expansion and higher diffusion rates of NaCl on Ag(1 0 0). The best epitaxy, i.e. that with the highest selectivity of a specific azimuthal domain orientation, is achieved by growing NaCl films at low deposition rate (0.1 ML min⁻¹) on the Ag(1 0 0) substrate at constant high temperature (450–500 K). The observations made here can probably be applied more generally to other heterogeneous interfaces and, in particular, be used to improve the quality of thin insulating films.     

Scanning tunnelling microscopy studies of growth morphology in highly epitaxial c-axis oriented Pt thin film on (0 0 1) SrTiO3

A noble metal Pt thin film was successfully grown on (0 0 1) SrTiO₃ substrate by using a DC-sputtering technique. The surface morphology and growth features of the as-grown Pt films were investigated by scanning tunnelling microscopy. Growth conditions, such as pre-sputtering, deposition ambience, and oxygen ratio are found to greatly affect the orientation, the crystallinity, and the epitaxial behavior of Pt films on (0 0 1) SrTiO₃. Single-crystalline Pt films have been achieved by introducing a few percentage oxygen into the sputtering ambient. The in-plane-relationship of the c-axis oriented Pt thin films on (0 0 1) SrTiO₃ was determined to be (0 0 1)_Pt∥(0 0 1)_SrTiO3 and [0 0 1]_Pt∥[0 0 1]_SrTiO3. Oxygen in the sputtering ambient was found to be a key factor to achieve the epitaxial Pt films.     

Growth of ultrathin layers of Au on LiNbO3(0 0 0 1) measured with atomic force microscopy

Atomic force microscopy (AFM) has been used to characterize the growth of Au deposited via evaporation onto the positive face of single crystalline, lithium niobate, LiNbO₃(0 0 0 1) surface. In order to study the mechanisms for the ordering and aggregation of a noble metal on this ferroelectric surface, topographic and phase contrast imaging of the fractional surface coverage of Au were performed. Atomically flat, uniformly poled LiNbO₃ surfaces were prepared via an ambient high temperature anneal and served as a support for the thin gold films. These gold atomic layers were grown using electron bombardment evaporation sources under ultra-high vacuum (UHV) conditions and subsequently characterized under both vacuum and ambient environments. Using AFM it was found that gold preferentially nucleates at the top of LiNbO₃ substrate step edges. With increased coverage, island formation proceeds due to local aggregation of adsorbed gold on each substrate terrace. Based on local imaging of the growth morphology, the data is discussed in terms of thin film growth mechanisms as well as the influence of native surface features such as defects and charge distribution. Understanding growth mechanisms for gold layers on ferroelectric surfaces allows for a fuller appreciation of how atomic deposition of metal atoms on patterned poled LiNbO₃ surfaces would occur as well as yielding greater insight on the atomic characteristics of metals on ferroelectric interfaces.     

Growth,structure, and thermal stability of epitaxial BaTiO3 films on Pt(111)

The growth of epitaxial ultrathin BaTiO₃ films upon rf magnetron sputter deposition on a Pt(111) substrate has been studied by scanning tunnelling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The BaTiO₃ films have been characterized from the initial stages of growth up to a film thickness of 4 unit cells. The deposited films develop a long-range order upon annealing at 1050 K in UHV. In the submonolayer regime a wetting layer is formed on Pt(111). Thicker films reveal a Stranski–Krastanov-like structure as observed with STM. By XPS a good agreement of the thin film stoichiometry with BaTiO₃ single crystal data is determined. Due to annealing at 1150 K BaTiO₃ forms large two-dimensional islands on the Pt(111) substrate. Different surface structures develop on the islands depending on the O₂ partial pressure during annealing.     

Growth and characterization of CoSi2 films on Si (1 0 0) substrates

In the present work, a special solid phase epitaxy method has been adapted for the preparation of CoSi₂ film. This method includes an epitaxial growth of Co films on Si (1 0 0) substrate, and in situ annealing of the Co/Si films in vacuum. It has been found that at the substrate temperature of 360°C, fcc cobalt film grows epitaxially on the Si (1 0 0) surface. The crystallographic orientation relations between fcc Co film and Si substrate determined from the electron diffraction result are: (0 0 1) Co//(0 0 1) Si, [1 0 0] Co//[1 1 0]Si. Upon annealing at temperatures range from 500 to 600°C, Co film reacts with Si substrate and transforms into CoSi₂. The CoSi₂ films prepared by this way are characterized by XTEM, XPS and AFM.     

Epitaxial growth of Au and Pt on Fe3O4(1 1 1) surface

We have studied the epitaxial growth of Au and Pt layers on Fe₃O₄(1 1 1) as a function of the deposition temperature and thickness. The layers were deposited by UHV sputtering and the structural properties were investigated by reflection high energy electron diffraction (RHEED), X-ray experiments and transmission electron microscopy (TEM). The epitaxial growth of both metals was obtained whatever the deposition conditions but the wetting is however different for the two metals. Comparison between the coverage ratios of Au and Pt is correlated with their surface and interfaces energies. The optimum conditions to achieve a 2D flat epitaxial metallic layer are determined.     

Epitaxial growth of Al on Si(1 1 1) with Cu buffer layers

The structure of thin Al films grown on Si(1 1 1) with thin Cu buffer layers has been investigated using synchrotron radiation photoemission spectroscopy. A thin Cu(1 1 1) layer between the Si(1 1 1) substrate and an Al film may enhance quantum well effects in the Al film significantly. The strength of quantum well effects has been investigated qualitatively with respect to the thickness of the Cu buffer layer and to the Al film thickness. Deposition of Cu on Si(1 1 1)7 × 7 leads to formation of a disordered silicide layer in an initial regime before a well-ordered Cu(1 1 1) film is formed after deposition of the equivalent of 6 layers of Cu. In the regime below 6 layers of Cu the disorder is transferred to Al layers subsequently grown on top. The initial growth of up to 8 layers of Al on a well-ordered Si/Cu(1 1 1) layer leads to a disordered film due to the lattice mismatch between the two metals. When the Cu buffer layer and the Al over-layer are above 6 and 8 layers, respectively the Al film shows sharp low energy electron diffraction patterns and very sharp quantum well peaks in the valence band spectra signalling good epitaxial growth.     

Study on structural properties of epitaxial silicon films on annealed double layer porous silicon

In this paper, epitaxial silicon films were grown on annealed double layer porous silicon by LPCVD. The evolvement of the double layer porous silicon before and after thermal annealing was investigated by scanning electron microscope. X-ray diffraction and Raman spectroscopy were used to investigate the structural properties of the epitaxial silicon thin films grown at different temperature and different pressure. The results show that the surface of the low-porosity layer becomes smooth and there are just few silicon-bridges connecting the porous layer and the substrate wafer. The qualities of the epitaxial silicon thin films become better along with increasing deposition temperature. All of the Raman peaks of silicon films with different deposition pressure are situated at 521 cm⁻¹ under the deposition temperature of 1100 °C, and the Raman intensity of the silicon film deposited at 100 Pa is much closer to that of the monocrystalline silicon wafer. The epitaxial silicon films are all (4 0 0)-oriented and (4 0 0) peak of silicon film deposited at 100 Pa is more symmetric.     

Growth of thin Fe(0 0 1) films for terahertz emission experiments

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.     

Modeling of In2O3-10 wt% ZnO thin film properties for transparent conductive oxide using neural networks

Effects of deposition process parameters on the deposition rate and the electrical properties of In₂O₃–10 wt% ZnO (IZO) thin films were modeled and analyzed by using the error back-propagation neural networks (BPNN). Output models were represented by response surface plots and the fitness of models was estimated by calculating the root mean square error (RMSE). The deposition rate of IZO thin films is affected by the RF power and the substrate temperature. The electrical properties of the IZO thin films are mainly controlled by O₂ ratio and the substrate temperature. The predicted output characteristics by BPNN can sufficiently explain the mechanism of IZO deposition process. Thus, neural network models can provide the reliable explanation of IZO film deposition.     

Atomic-level investigation of Al and Ni thin film growth on Ni(1 1 1) surface: Molecular dynamics simulation

Using molecular dynamics (MD) simulation, the structural characteristics of Al and Ni thin film growth on Ni(1 1 1) substrate according to the incident energy of adatoms were investigated. In case of Al on Ni(1 1 1), Al adatoms were grown basically through the layer-by-layer growth mode. On the other hand, Ni thin films on Ni(1 1 1) surface at low incident energy were shown to favor island growth. The steering effect due to atomic attraction, which results in rougher surface, was significantly observed at low incident energy. The growth mode of Ni film was, however, changed to follow layer-by-layer growth mode for the incident energy of 6 eV. The different aspects of surface morphology between Al and Ni deposition on Ni(1 1 1) surface could be successfully explained by the surface diffusion and impact cascade diffusion.     

A competition between (0 0 1) and (0 1 1) alignments in yttria stabilized zirconia thin films fabricated by ion beam assisted deposition

Biaxially textured yttria stabilized zirconia (YSZ) thin films, were deposited on glass substrates by ion beam assisted deposition method with different deposition time. As contrasts, films were also fabricated without assisting ion beam. The orientation properties of the films were characterized by X-ray diffraction. A comparative study shows that there is a competition between (0 0 1) and (0 1 1) alignments during the growth process. Assisting ions make the films (0 0 1)-advantaged and biaxially textured. The competitive growth and the orientation development are explained by selective resputtering and anisotropic damage on growing films induced by assisting ions.     

X-ray characterization of as-deposited, epitaxial films of Bi(0 1 2) on Au(1 1 1)

Electrodeposition is used to produce epitaxial single-crystal films on Au(1 1 1) substrates without annealing or other post-deposition modification. X-ray techniques show that the Bi(0 1 2) plane is parallel to the underlying Au(1 1 1) surface, and the azimuthal orientation of the films is determined. Combination of the X-ray data with in situ scanning tunneling microscopy (STM) images suggests a common growth mode from the first few layers up to thick films.     

Growth of Au thin film on Cu-modified Si(1 1 1) surface

Miniaturizing of electronic devices requires that conductive elements maintain advanced electrical characteristics upon reducing their geometrical sizes. For gold, which is valued for its high electrical conductivity and stability against ambient conditions, creation of extra-thin films on silicon is hampered by formation of the quite complex Au/Si interface. In the present work, by forming a Si(1 1 1)5.55 × 5.55-Cu surface reconstruction prior to Au deposition we formed Au films with smoother surface morphology and higher surface conductivity compared to Au film grown on a pristine Si(1 1 1)7 × 7 surface. Scanning tunnelling microscopy and four-point probe measurements were used to characterize the growth mode of the Au film on a Si(1 1 1)5.55 × 5.55-Cu reconstruction at room temperature.     

Electron microscope study of aluminium films evaporated on air-cleaved sodium chloride

The article deals with the structure of thin aluminium films evaporated on air-cleaved NaCl substrates. The effect of the substrate temperature and the film thickness on the structure, the orientation and the grain size of the films was studied at a deposition rate of 10 Å/see (ev. 50 Å/see) in a vacuum of about 7. 10^–5 torr. The optimum temperature for epitaxial growth was found to be about 420°C. An almost regular arrangement of grains was found in the thickness region of 90–150 Å.     

Epitaxial growth of bcc Fe films on Al(1 0 0) surfaces using Ti as an interface stabilizer

An approach is described to promote epitaxial growth of thin metal films on single-crystal metal substrates by stabilizing the interface with an extremely thin metallic interlayer. A single atomic layer of a metal is deposited at the interface, Ti on Al(1 0 0) in this case, prior to the growth of the metal film of interest to produce an epitaxial interface in a system that is otherwise characterized by interdiffusion and disorder. The stabilized interface reduces interdiffusion and serves as a template for ordered film growth. Using Rutherford backscattering and channeling techniques along with low-energy electron diffraction and low-energy He⁺ scattering, it is demonstrated that an atomically thin layer of Ti metal deposited at the Fe-Al interface, a system well known for considerable intermixing at room temperature, reduces interdiffusion and promotes the epitaxial growth of Fe films on the Al(1 0 0) surface. The decrease in ion scattering yield for Al atoms, Fe-Fe shadowing and long-range order of the surface suggest that the epitaxial growth of Fe is greatly improved when the Ti interlayer is introduced prior to Fe deposition. Off-normal ion channeling experiments provide clear evidence for the bcc structure of Fe on the Ti/Al(1 0 0) template with the measured average (1 0 0) interplanar distance of 1.44 Å in the Fe overlayer.     

Ultra-thin film growth of titanium dioxide on W(1 0 0)

We have employed low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy to follow the epitaxial growth of thin films of TiO₂ on W(1 0 0). The films were grown both by metal vapour deposition of titanium onto the substrate in UHV with subsequent annealing in a low partial pressure of oxygen, and by metal vapour deposition in a low partial pressure of oxygen. LEED patterns showed the characteristic patterns of (1 1 0) oriented rutile. A systematic spot splitting was observed and attributed to a stepped surface. The calculated step height was found to be in good agreement with that expected for rutile TiO₂(1 1 0), 3.3 Å. Titanium core level shifts were used to identify oxidation states as a function of film thickness allowing the interpretation in terms of a slightly sub-stoichiometric interface layer in contact with the substrate. In combination with the LEED patterns, the film structure is therefore determined to be (1 1 0) oriented rutile with a comparable level of stoichiometry to UHV prepared bulk crystals. The ordered step structure indicates considerable structural complexity of the surface.     

From bilayer to monolayer growth: Temperature effects in the growth of Ru on Pt(1 1 1)

At temperatures around 373 K, Ru growth on Pt(1 1 1) proceeds via nucleation and growth of bilayer islands [H.E. Hoster et al., Phys. Chem. Chem. Phys. 3 (2001) 337]. The influence of the deposition temperature on the Ru growth behavior on Pt(1 1 1) was studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) in the temperature range between 303 and 773 K. The data reveal a distinct change in the growth characteristics, most important the change from the growth of bilayer Ru islands to monolayer islands, at temperatures between 523 and 573 K. Based on AES data and on atomic resolution STM images, these changes are associated with the onset and increasing contribution of surface alloy formation via Pt–Ru exchange and, at T > 673 K, alloy formation in near surface regions. Consequences of these data for the mechanism of bilayer growth and the underlying physical origin are discussed.     

Growth and morphology of the epitaxial Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) Trilayers

Growth and surface morphology of epitaxial Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) trilayers constituting a magnetic tunnel junction were investigated by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). STM reveals a grain-like growth mode of MgO on Fe(1 1 0) resulting in dense MgO(1 1 1) films at room temperature as well as at 250 °C. As observed by STM, initial deposition of MgO leads to a partial oxidation of the Fe(1 1 0) surface which is confirmed by Auger electron spectroscopy. The top Fe layer deposited on MgO(1 1 1) at room temperature is relatively rough consisting of clusters which can be transformed by annealing to an atomically flat epitaxial Fe(1 1 0) film.